This invention relates in general to planocentric gear drives. More specifically, this invention relates to an improved planocentric gear drive for use as a simplified and inexpensive stepping motor with an output rotatable in relatively small angular increments and locked against rotation when not in use.
Planocentric gear drives in general are known in the art and typically comprise at least two meshing coplanar gears designed to convert a rotary drive input to a rotary output with substantial speed reduction. Such gear drives commonly include a rotatable driving gear in meshing engagement with a fixed stator gear, and driven by the rotary input in an eccentric or orbital path about the axis of the stator gear. By appropriate selection of the relative numbers of teeth on the driving and stator gears, the driving gear rotates about its own axis relatively slowly with respect to the number of its orbital revolutions about the axis of the stator gear to provide a relatively slow speed rotary motion which can be coupled to an output shaft, an output gear, or the like.
A variety of specific planocentric gear drive configurations have been proposed for accommodating different types of rotary input and rotary output structures in different operating environments. For example, some planocentric gear drives have been developed wherein the driving gear is eccentrically driven in meshing engagement with the stator gear by a rotating mechanical drive shaft, such as those shown and described in U.S. Pat. Nos. 107,432 and 2,508,121. Other planocentric gear drives have been proposed including electromagnetic systems for moving the driving gear in an orbital path about the axis of the stator gear. See, for example, U.S. Pat. Nos. 3,456,139; 3,561,006; Re. 27,446; and 3,894,255.
The use of electromagnetic systems for orbitally moving the driving gear advantageously simplifies the planocentric gear drive by eliminating the mechanical drive shaft and its attendant bearings, drive means, and the like. Moreover, electromagnetic systems facilitate operation of the gear drive as a stepping motor wherein the rotary output is moved through relatively small angular increments. For example, some electromagnetic systems utilize a plurality of circumferentially arranged electromagnets energized in sequence to orbit the driving gear in steps, and thereby provide the desired incrementally stepped output. However, positive engagement between the gears ceases when power to the electromagnets is turned off to permit the gears to be rotated relative to each other. Alternately stated, the gears are not locked in position when the planocentric gear drive is not in use, thereby permitting the rotary output to be moved freely with respect to the stator gear. In many operating environments, this failure to lock the gears in position when the planocentric gear drive is not in use is highly undesirable.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved planocentric gear drive for providing a rotary output in the form of relatively small incremental steps wherein the components of the gear drive are locked in position with respect to each other when the gear drive is not in use.